3 Answers
3

There is a method that pretty much allows you to do this without thinking at all:

In photoshop:

IF necessary, Ctrl+L and bring the upper white arrow to the center enough, so that you will get white background ( Also, you might want to bring the top black arrow towards the center to make the black colors black ) ( This step is not necessary in this case ).

Select the Brush tool.

From the top menu: Edit > Define brush preset ( Since the Brush tool was selected ), the created brush will straight away be selected.

Create a new document Ctr+N without the background color ( make it bigger than the original image, so you don't have to aim much ).

Click D ( to default the foreground color to black ).

Click once in the document to place the image in the brush.

From the top menu: Image > Trim > Base on: Transparent pixels

It may seem like this has big amount of steps, but you can do this very, very fast.